Methods and systems for providing enhanced position location in wireless communications

ABSTRACT

Embodiments disclosed herein relate to methods and systems for providing improved position location (e.g., time-of-arrival) measurement and enhanced position location in wireless communication systems. In an example method, an access terminal may receive a reference signal in a time slot, the reference signal comprising a sequence of symbols known to a receiver before being received, and may determine, based at least in part on the reference signal, a position location of the access terminal.

The present application is a continuation of U.S. patent applicationSer. No. 14/288,971, entitled “METHODS AND SYSTEMS FOR PROVIDINGENHANCED POSITION LOCATION IN WIRELESS COMMUNICATIONS”, filed May 28,2014, now allowed, which is divisional of U.S. patent application Ser.No. 13/024,230, entitled “METHODS AND SYSTEMS FOR PROVIDING ENHANCEDPOSITION LOCATION IN WIRELESS COMMUNICATIONS”, filed Feb. 9, 2011,issued as U.S. Pat. No. 8,773,308, which is a continuation applicationof U.S. patent application Ser. No. 11/313,321, entitled “METHODS ANDSYSTEMS FOR PROVIDING ENHANCED POSITION LOCATION IN WIRELESSCOMMUNICATIONS”, filed Dec. 20, 2005, issued as U.S. Pat. No. 7,893,873,the entireties of which all are incorporated by reference herein.

FIELD

This disclosure relates generally to wireless communications. Morespecifically, embodiments disclosed herein relate to providing improvedtime-of-arrival measurement and enhanced position location in wirelesscommunication systems.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustypes of communications (such as voice and data) to multiple users. Suchsystems may be based on code division multiple access (CDMA), timedivision multiple access (TDMA), frequency division multiple access(FDMA), or other multiple access techniques. A wireless communicationsystem may be designed to implement one or more standards, such asIS-95, cdma2000, IS-856, W-CDMA, TD-SCDMA, and other standards.

Presence detection and location-based services have long been soughtafter in wireless communications. In addition to supporting emergencyservices (e.g., E911 calls), wireless operators are striving to providea wide range of new applications targeted for the everyday consumer andenterprise user, such as child locators, turn-by-turn navigation,directory services, voice concierge, roadside assistance, and manyothers. A challenge hence lies in providing accurate and reliableposition location to enable such applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of a wireless communication system;

FIG. 2 illustrates an embodiment of forward link slot structure in anIS-856 type system;

FIGS. 3A-3B illustrate embodiments of forward link slot structure forreference transmission;

FIG. 4A illustrates an embodiment of forward link structure in an IS-95type system;

FIG. 4B illustrates an embodiment of forward link structure forreference transmission;

FIG. 5 illustrates a flow diagram of a process, which may be used toimplement some disclosed embodiments;

FIG. 6 illustrates a flow diagram of a process, which may be used toimplement some disclosed embodiments;

FIG. 7 illustrates a flow diagram of a process, which may be used toimplement some disclosed embodiments;

FIG. 8 illustrates a flow diagram of a process, which may be used toimplement some disclosed embodiments;

FIG. 9 illustrates a block diagram of an apparatus, in which somedisclosed embodiments may be implemented; and

FIG. 10 illustrates a block diagram of an apparatus, in which somedisclosed embodiments may be implemented.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to methods and systems for providingenhanced position location in wireless communication systems.

An access point (AP) disclosed herein may include and/or implementfunctions of a base-station transceiver system (BTS), an access networktransceiver (ANT), a modem pool transceiver (MPT), or a Node B (e.g., ina W-CDMA type system), etc. A cell may refer to a coverage area servicedby an AP. A cell may further include one or more sectors. For simplicityand clarity, the term “sector” may be used herein to refer a cell, or asection of a cell, serviced by an AP. Further, an access networkcontroller (ANC) may refer to the portion of a communication systemconfigured to interface with a core network (e.g., a packet datanetwork) and route data packets between access terminals (ATs) and thecore network, perform various radio access and link maintenancefunctions (such as soft handoff), control radio transmitters andreceivers, and so on. An ANC may include and/or implement the functionsof a base station controller (BSC), such as found in a 2^(nd), 3^(rd) or4^(th) generation wireless network. An ANC and one or more APs mayconstitute part of an access network (AN).

An access terminal (AT) described herein may refer to various types ofdevices, including (but not limited to) a wireless phone, a cellularphone, a laptop computer, a multimedia wireless device, a wirelesscommunication personal computer (PC) card, a personal digital assistant(PDA), an external or internal modem, etc. An AT may be any data devicethat communicates through a wireless channel and/or through a wiredchannel (e.g., by way of fiber optic or coaxial cables). An AT may havevarious names, such as access unit, access node, subscriber unit, mobilestation, mobile device, mobile unit, mobile phone, mobile, remotestation, remote terminal, remote unit, user device, user equipment,handheld device, etc. Different ATs may be incorporated into a system.ATs may be mobile or stationary, and may be dispersed throughout acommunication system. An AT may communicate with one or more APs on aforward link and/or a reverse link at a given moment. The forward link(or downlink) refers to transmission from an AP to an AT. The reverselink (or uplink) refers to transmission from the AT to the AP.

Locating a person or an object wirelessly may be achieved in a number ofways. Time-of-arrival (TOA) measurement, which uses time it takes for asignal to travel as an indirect method of calculating distance, iscommonly involved in a number of network-based methods. For example, insome wireless networks, position location services require TOAmeasurement of the pilot signal (e.g., the earliest path of the pilot).

FIG. 1 illustrates a wireless communication system 100 configured tosupport a number of users, in which various disclosed embodiments andaspects may be implemented, as further described below. By way ofexample, system 100 provides communication for a number of cells 102,including cells 102 a-102 g, with each cell being serviced by acorresponding AP 104 (such as APs 104 a-104 g). Each cell may be furtherdivided into one or more sectors. Various ATs 106, including ATs 106a-106 k, are dispersed throughout the system. Each AT 106 maycommunicate with one or more APs 104 on a forward link and/or a reverselink at a given moment, depending upon whether the AT is active andwhether it is in soft handoff, for example.

In FIG. 1, a solid line with an arrow may indicate information (e.g.,data) transmission from an AP to an AT. A broken line with an arrow mayindicate that the AT is receiving the pilot and othersignaling/reference signals, but no data transmission, from the AP, asfurther described below. For clarity and simplicity, the reverse linkcommunication is not explicitly shown in FIG. 1.

In a high rate packet data (HRPD) system (e.g., as specified in“cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2C.S0024-A, Version 2, July 2005, referred to as “1×EV-DO” (or “IS-856”)herein), for example, transmission on forward link is partitioned into asequence of frames; each frame is further divided into time slots (e.g.,16 slots each with a duration of 1.667 msec); and each slot includes aplurality of time-division-multiplexed channels.

By way of example, FIG. 2 illustrates an embodiment of a forward linkslot structure 200, such as employed in a 1×EV-DO type system. Time slot200 is divided into two half-slots, with each half-slot having thefollowing channel assignments: pilot channel 210, forward medium accesscontrol (MAC) channel 220, and forward traffic (or control) channel 230.Pilot channel 210 carries the pilot signal (also commonly termed as thepilot) used by an AT (such as AT 106 in FIG. 1) for initial acquisition,phase recovery, timing recovery, radio combining, as well as estimatingthe channel conditions on forward link (e.g., by way of thesignal-to-noise-and-interference (SINR) measurement). MAC channel 220sets forth the procedures used to receive and transmit over the physicallayer (which provides the channel structure, frequency, power output,modulation, encoding specifications for forward and reverse links).Traffic channel 230 may carry information or data (e.g., by way ofphysical layer packets), e.g., unicast data specific to a particular AT(or user), or broadcast/multicast data to a group of users (e.g., asspecified in “cdma2000 High Rate Broadcast-Multicast Packet Data AirInterface Specification,” 3GPP2 C.S0054-0, Version 2.0, July 2005,referred to as “BCMCS specification” herein). Traffic channel 230 mayalso be used to carry control messages. Further, pilot channel 210, MACchannel 220, and traffic channel 230 are time-division-multiplexedwithin time slot 200. When there is no traffic on traffic channel 230,an idle slot including pilot channel 210 and MAC channel 220 may besent. Transmission of idle slots serves to decrease interference toother cells on forward link.

As illustrated in FIG. 2, pilot channel 210 is transmitted in discretebursts (as opposed to being continuous in time), hence having limitedpower. In some systems, for example, pilot channel 210 may comprise 96chips of a particular digital pattern (e.g., all zeros), MAC channel 220may comprise 64 chips, and each half-slot may comprise 1024 chips. Thus,only a small fraction (e.g., 96/1024) of the available forward linkpower is allotted to the pilot channel in such systems. As a result, TOAmeasurement based on such pilot channel may be susceptible to errors(e.g., particularly when the forward link channel conditions are poor),hence, compromising the accuracy and reliability of associated positionlocation. A need therefore exists for a strong and clear signal toassist position location.

Embodiments disclosed herein relate to methods and systems for providingimproved TOA measurement and enhanced position location in wirelesscommunication systems.

In an embodiment, an AP may replace normal information (e.g., data)transmission by a “known” transmission (termed “reference transmission”herein) at a predetermined time known to ATs in sectors serviced by theAP. The ATs may use the received reference transmission to assist orfacilitate position location (e.g., TOA and/or other position-locationmeasurements). The AP may also send a reference transmission on demand,e.g., in response to a request from an AT (which may be in need for alocation-based service).

In some embodiments, the reference transmission may include a time slothaving a pilot signal and a reference signal in atime-division-multiplexed format. In other embodiments, the referencetransmission may include a time slot having a pilot signal and areference in a code-division-multiplexed format. The reference signalmay be similar or substantially identical to the pilot, such that theentire time slot is nearly filled with the pilot, thereby providing astrong signal for TOA and other position-location measurements. Thereference signal may also be different from the pilot, e.g., configuredto assist the pilot in position location. The ensuing descriptionprovides further embodiments and examples.

The term “reference signal” disclosed herein may include any signal thatis unmodulated (e.g., carrying no information or data) and known to areceiving AT. For example, the reference signal may comprise a digitalpattern (e.g., a sequence of symbols) that is “known” in advance to thereceiving AT, whereby the AT does not need to decode the referencesignal. The reference may carry a unique sector ID (e.g., spread with apseudorandom (PN) code with a unique offset specific to the sector). Thereference signal may be transmitted at substantially the maximum poweravailable to the sector (or “full sector power”). In some embodiments,the reference signal may be a spread-spectrum or other wideband signal(e.g., to occupy the entire traffic channel). A “reference transmission”disclosed herein may refer to a forward link transmission including areference signal. Further, the term “position-location measurement” maybroadly refer to a measurement associated with position location,including (but not limited to) TOA, time difference of arrival (TDOA),angle of arrival (AOA), advanced forward link trilateration (AFLT),enhanced observed time difference (EOTD), and others.

Various aspects, features, and embodiments are described in furtherdetail below.

FIG. 3A illustrates an embodiment of a reference transmission includinga time slot 300, which may be used to implement some disclosedembodiments. Time slot 300 is shown in two half-slots, each having pilotchannel 310, MAC channel 320, and traffic channel 330 in atime-division-multiplexed format. Pilot channel 310 carries the pilot.Pilot channel 310 and MAC channel 320 may for example be substantiallyas described above with respect to the embodiment of FIG. 2. Trafficchannel 330 carries a reference signal, in lieu of data.

In some embodiments, the reference signal may be similar orsubstantially identical to the pilot, as time slot 350 of FIG. 3Billustrates. As a result, the entire slot 350 is nearly filled with thepilot, as graphically illustrated by the hatched area in the figure, andthe full power of the entire sector may be substantially devoted to thepilot transmission during this time period. This strong pilot allows thereceiving ATs to carry out more accurate and reliable TOA and otherposition-location measurements. The timing and signaling for such “pilotslot” may for example be according to the broadcast/multicast channelstructure in a 1×EV-DO type system (e.g., as specified in the BCMCSspecification). Further, implementation of such “pilot slot” imposesminimal changes to the existing network infrastructures and devices.

In other embodiments, the reference signal may be different from thepilot. The timing and signaling for the reference transmission may forexample be according to the broadcast/multicast channel structure in a1×EV-DO type system (e.g., as specified in the BCMCS specification). Inone embodiment, for example, the pilot may comprise a sequence ofsymbols having all zeros (0's), whereas the reference signal maycomprise a sequence of symbols having all ones (1's). In anotherembodiment, the pilot may comprise the pilot symbols used in a 1×EV-DOtype system, whereas the reference signal may comprise the pilot symbolsused in an IS-95 type system. In yet another embodiment, the pilot maycomprise a particular sequence of symbols, while the reference signalmay comprise the sequence configured in reverse. In an alternativeembodiment, a known data packet may be transmitted as the referencesignal, e.g., using the broadcast/multicast channel structure andsignaling in a 1×EV-DO type system (e.g., as specified in the BCMCSspecification). A receiving AT may use this reference signal to searchfor the (weaker) pilot, estimate TOA (and/or perform otherposition-location measurements), and report back the measuredinformation.

In an embodiment, the reference transmission may be carried out by an APaccording to a predetermined schedule (e.g., on a regular or periodicbasis), so that at known times, ATs in the corresponding sectors may beprepared to perform TOA and/or other position-location measurements, andreport back the measured information.

In an embodiment, an AP may carry out the reference transmission ondemand, e.g., upon receiving a request from an AT (which may be in needfor a location-based service).

In an embodiment, an AP may make use of idle slots for referencetransmission (e.g., filing an idle slot substantially with the pilot,such as described above with respect to the embodiment of FIG. 3B), soas to make efficient use of the network resources. For example, thesignaling associated with such time slot may indicate to a receiving ATthe reference signal carried by the traffic channel, so that the AT mayaccordingly perform TOA and/or other position-location measurements.

FIGS. 3A-3B provide some examples of transmitting a reference signalalong the pilot in a time-division-multiplexed format. In other systems(e.g., as specified in “Physical Layer Standard for cdma2000 SpectrumSystems,” 3GPP2 C.S0002-D, Version 2.0, September 2005, referred to as“CDMA2000 1×” herein, or as specified in “Mobile Station-Base StationCompatibility Standard for Wideband Spread Spectrum Cellular Systems,”ANSI/TIA/EIA-95-B-99, referred to as “IS-95” herein), a reference signalmay be transmitted along with the pilot in a code-division-multiplexedformat, such as described below.

FIG. 4A illustrates an embodiment of forward link structure in the formof sector power usage vs. time, such as in an IS-95 or CDMA2000 1×typesystem. Forward link channels, including pilot channel 410, sync channel420, paging channel 430, and traffic channels 440, are transmitted in acode-division-multiplexed format, each with a certain fraction of thetotal sector power. For example, pilot channel 410 may be allottedapproximately 15-20% of the maximum sector power, denoted asP_(Tx)(max). To augment the pilot (e.g., for position locationpurposes), some or all of the power allotted to traffic channels 440 maybe used to transmit a reference signal (in lieu of informationtransmission) in a specific period of time, such as illustrated in FIG.4B below.

For illustration and clarity, FIG. 4B depicts an embodiment in which thepower allotted to traffic channels 440 may be substantially devoted totransmit a reference signal 460 in a time slot 450. For example, suchmay occur in situations where an AP sends a reference transmission tothe corresponding ATs according to a predetermined schedule (e.g., on aregular or periodical basis), so that at known times, the ATs may beprepared to perform position-location measurements and report back themeasured information. In some embodiments, the reference signal may besimilar or substantially identical to the pilot; as a result, the entiretime slot 450 may be nearly filled with the pilot, thereby providing astrong signal for position-location measurements. In other embodiments,the reference may also be different from the pilot, such as describedabove.

In alternative embodiments, a fraction of the power allotted to trafficchannels 440 may be used to transmit reference signal 460 in time slot450. For example, such may occur in situations where an AP carries out areference transmission on demand, e.g., in response to request(s) fromone or more ATs in the corresponding sectors (which may be in need forposition-location services).

In addition to replacing information transmission by a referencetransmission according to a predetermined schedule or on demand (such asdescribed above), a portion of the control channel (e.g., the preamble),or other existing (or known) signals, may be used to assist the pilot inposition location. For example, in some systems, the control channel maybe transmitted on a regular or periodic basis. The preamble of thecontrol channel may be known to a receiving AT (e.g., after the initialset-up), and therefore, used to assist the pilot in position location(such as in a manner described above with respect to the referencesignal).

FIG. 5 illustrates a flow diagram of a process 500, which may be used toimplement some disclosed embodiments (such as described above). Step 510generates a pilot signal and a reference signal, the reference signalcomprising a sequence of symbols known to an access terminal. Step 520transmits the pilot signal and the reference signal in a time slot.

In process 500, the pilot signal and the reference signal may betransmitted in a time-division-multiplexed format orcode-division-multiplexed format, such as described above. In someembodiments, the reference signal may be similar or substantiallyidentical to the pilot signal. In other embodiments, the referencesignal may be different from the pilot signal, e.g., configured toassist the pilot signal in position location (e.g., TOA and otherposition-location measurements), such as described above. Further, in amulti-carrier wireless communication system, the time slot may betransmitted on a subset (e.g., some, all, or any combination) ofcarriers.

FIG. 6 illustrates a flow diagram of a process 600, which may be used toimplement some disclosed embodiments (such as described above). Process600 starts at step 610. Step 620 determines (e.g., based on apredetermined schedule) whether it is time for carrying out a referencetransmission to ATs in sectors serviced by an AP. If the outcome of step620 is “YES,” step 630 follows and generates a pilot signal and areference signal. Step 640 transmits the pilot signal and the referencesignal in a time slot (e.g., in a time-division-multiplexed orcode-division-multiplexed format, such as described above).Subsequently, process 600 returns to step 620.

In process 600, if the outcome of step 620 is “NO,” step 650 follows anddetermines if there is a request for a location-based service from anAT. If the outcome of step 650 is “YES,” process 600 returns to step630. If the outcome of step 650 is “NO,” step 660 follows and proceedswith information (e.g., data) transmission. Process 600 subsequentlyreturns to step 620.

FIG. 7 illustrates a flow diagram of a process 700, which may be used toimplement some disclosed embodiments. Step 710 receives a pilot signaland a reference signal in a time slot (e.g., in atime-division-multiplexed or code-division-multiplexed format, such asdescribed above). Step 730 performs a position-location measurementbased on the pilot signal and the reference signal.

Process 700 may further include searching for the pilot signal. In someinstances, the reference signal may be similar or substantiallyidentical to the pilot signal, effectively providing a strong pilot forposition-location measurements. In other instances, a receiving AT mayuse the reference signal to search for the (weaker) pilot, estimate TOA(and/or perform other position-location measurements), and report backthe measured information.

FIG. 8 illustrates a flow diagram of a process 800, which may be used toimplement some disclosed embodiments (such as described above). Process800 starts at step 810. Step 820 receives a time slot having a pilotchannel and a reference channel (e.g., in a time-division-multiplexedformat, such as described above), the pilot channel carrying a pilotsignal. Step 830 determines if the traffic channel carries a referencesignal. If the outcome of step 830 is “YES,” step 840 follows andperforms a position-location (e.g., TOA) measurement based on the pilotsignal and the reference signal. Process 800 subsequently returns tostep 820. If the outcome of step 830 is “NO,” step 850 follows andproceeds with the traffic channel (e.g., decode the data packets carriedby the traffic channel). Process 800 subsequently returns to step 820.

FIG. 9 shows a block diagram of an apparatus 900, which may be used toimplement some disclosed embodiments (such as described above). By wayof example, apparatus 900 may include a reference-generating unit (ormodule) 910 configured to generate a pilot signal and a referencesignal, wherein the reference signal comprising a sequence of knownsymbols (e.g., to one or more receiving ATs); and a transmitting unit930 configured to transmit the pilot signal and the reference signal ina time slot. In a multi-carrier system, transmitting unit 930 may befurther configured to transmit the time slot on a subset of carriers.

Apparatus 900 may also include a multiplexing unit 920 configured tomultiplex the pilot signal and the reference signal into the time slot(e.g., in a time-division-multiplexed or code-division-multiplexedformat, such as described above). Apparatus 900 may further include aprocessing unit (or controller) 940 configured to control and/orcoordinate the operations of various units.

Apparatus 900 may be implemented in an AP (e.g., AP 106 in FIG. 1), orother network infrastructure elements.

FIG. 10 illustrates a block diagram of an apparatus 1000, which may alsobe used to implements some disclosed embodiments (such as describedabove). By way of example, apparatus 1000 may include a receiving unit1010 configured to receive a pilot signal and a reference signal in atime slot (e.g., in a time-division-multiplexed orcode-division-multiplexed format, such as described above); and ameasurement unit 1030 configured to perform a position-location (e.g.,TOA) measurement based on the pilot signal and the reference signal.Apparatus 1000 may further include a searching unit 1020, configured tosearch for the pilot signal. Apparatus 1000 may also include aprocessing unit (or controller) 1040, configured to control and/orcoordinate the operations of various units

Apparatus 1000 may be implemented in an AT, or other communicationdevices.

Embodiments disclosed herein (such as described above) provide someembodiments for enhancing position location in wireless communications.There are other embodiments and implementations.

Embodiments disclosed herein may be applied to a multi-carrier wirelesscommunication system. For example, a reference transmission may be senton some, all, or any combination of carriers.

Various units/modules in FIGS. 9-10 and other embodiments may beimplemented in hardware, software, firmware, or a combination thereof.In a hardware implementation, various units may be implemented withinone or more application specific integrated circuits (ASIC), digitalsignal processors (DSP), digital signal processing devices (DSPDs),field programmable gate arrays (FPGA), processors, microprocessors,controllers, microcontrollers, programmable logic devices (PLD), otherelectronic units, or any combination thereof. In a softwareimplementation, various units may be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The software codes may be stored in a memory unit and executedby a processor (or a processing unit). The memory unit may beimplemented within the processor or external to the processor, in whichcase it can be communicatively coupled to the processor via variousmeans known in the art.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module may reside in random access memory (RAM), flashmemory, read only memory (ROM), electrically programmable ROM (EPROM),electrically erasable programmable ROM (EEPROM), registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in an AT. In the alternative, the processorand the storage medium may reside as discrete components in an AT.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. An access terminal (AT), comprising: a receivingunit configured to receive a reference signal in a time slot, thereference signal comprising a sequence of symbols known to the AT beforebeing received; and a measurement unit configured to determine aposition location of the AT based at least in part on the referencesignal.
 2. The AT of claim 1, wherein the receiving unit is furtherconfigured to receive a pilot signal on a pilot channel in the timeslot, wherein the reference signal is on a traffic channel in the timeslot.
 3. The AT of claim 2, wherein determining the position location ofthe AT is further based on the pilot signal.
 4. The AT of claim 3,wherein the pilot signal and the reference signal aretime-division-multiplexed.
 5. The AT of claim 3, wherein the pilotsignal and the reference signal are code-division-multiplexed.
 6. The ATof claim 2, wherein a pattern of the pilot signal is the same as apattern of the reference signal.
 7. The AT of claim 1, whereindetermining the position location of the AT comprises using timedifference of arrival (TDOA) measurements.
 8. The AT of claim 1, whereindetermining the position location of the AT comprises performing aposition location measurement.
 9. The AT of claim 1, wherein thereceiving unit is further configured to receive the reference signal ona periodic basis.
 10. A method for wireless communications, comprising:receiving at an access terminal (AT) a reference signal in a time slot,the reference signal comprising a sequence of symbols known to areceiver before being received; and determining a position location ofthe AT based at least in part on the reference signal.
 11. The method ofclaim 10, further comprising receiving a pilot signal on a pilot channelin the time slot, wherein the reference signal is on a traffic channelin the time slot.
 12. The method of claim 11, wherein determining theposition location of the AT is further based on the pilot signal. 13.The method of claim 12, wherein the pilot signal and the referencesignal are time-division-multiplexed.
 14. The method of claim 12,wherein the pilot signal and the reference signal arecode-division-multiplexed.
 15. The method of claim 11, wherein a patternof the pilot signal is the same as a pattern of the reference signal.16. The method of claim 10, wherein determining the position location ofthe AT comprises using time difference of arrival (TDOA) measurements.17. The method of claim 10, wherein determining the position location ofthe AT comprises performing a position location measurement.
 18. Themethod of claim 10, wherein receiving the reference signal is on aperiodic basis.
 19. An access terminal (AT), comprising: means forreceiving a reference signal in a time slot, the reference signalcomprising a sequence of symbols known to the AT before being received;and means for determining a position location of the AT based at leastin part on the reference signal.
 20. The AT of claim 19, furthercomprising means for receiving a pilot signal on a pilot channel in thetime slot, wherein the reference signal is on a traffic channel in thetime slot.
 21. The AT of claim 20, wherein determining the positionlocation of the AT is further based on the pilot signal.
 22. The AT ofclaim 21, wherein the pilot signal and the reference signal aretime-division-multiplexed.
 23. The AT of claim 21, wherein the pilotsignal and the reference signal are code-division-multiplexed.
 24. TheAT of claim 20, wherein a pattern of the pilot signal is the same as apattern of the reference signal.
 25. The AT of claim 19, wherein themeans for determining the position location of the AT comprises meansfor using time difference of arrival (TDOA) measurements in determiningthe position location.
 26. The AT of claim 19, wherein the means fordetermining the position location of the AT comprises means forperforming a position location measurement.
 27. The AT of claim 19,wherein the means for receiving the reference signal comprises means forreceiving the reference signal on a periodic basis.
 28. A non-transitorycomputer-readable medium for wireless communications, the medium storingone or more programs containing instructions that, when executed by aprocessor of an access terminal (AT), cause the AT to perform operationscomprising: receiving a reference signal in a time slot, the referencesignal comprising a sequence of symbols known to the AT before beingreceived; and determining a position location of the AT based at leastin part on the reference signal.
 29. The non-transitorycomputer-readable medium of claim 28, wherein execution of theinstructions further causes the AT to receive a pilot signal on a pilotchannel in the time slot, wherein the reference signal is on a trafficchannel in the time slot.
 30. The non-transitory computer-readablemedium of claim 29, wherein determining the position location of the ATis further based on the pilot signal.
 31. The non-transitorycomputer-readable medium of claim 30, wherein the pilot signal and thereference signal are time-division-multiplexed.
 32. The non-transitorycomputer-readable medium of claim 30, wherein the pilot signal and thereference signal are code-division-multiplexed.
 33. The non-transitorycomputer-readable medium of claim 29, wherein a pattern of the pilotsignal is the same as a pattern of the reference signal.
 34. Thenon-transitory computer-readable medium of claim 28, wherein executionof the instructions for determining the position location of the ATcauses the AT to use time difference of arrival (TDOA) measurements indetermining the position location.
 35. The non-transitorycomputer-readable medium of claim 28, wherein execution of theinstructions for determining the position location of the AT causes theAT to perform a position location measurement.
 36. The non-transitorycomputer-readable medium of claim 28, wherein execution of theinstructions for receiving the reference signal causes the AT to receivethe reference signal on a periodic basis.